When sawing concrete, brick, stone, wood, plasterboards and similar materials, dust is generated, usually large amounts thereof Many devices of different type are employed in order to prevent, as far as that is possible, but the dust is scattered to the environment, while other devices have been suggested but have not been used. Thus devices exist, whose mode of working, according to a known principle, makes use of a hood-shaped blade guard or the like, which surrounds the saw blade and in which dust is collected and is sucked away to a vacuum device via a hose, which is connected to the blade guard. A machine and a device of that kind is disclosed in WO 02/100597. It is typical and necessary that this known hood-shaped blade guard completely surrounds that part of the saw blade which is not located in the work piece, and that the blade guard contacts the surface of the work piece, which surface is supposed to be essentially flat, and with good sealing action, in order that the device shall function well as a dust collector. The blade guard thus shall function like a suction box, in which a sufficient under pressure must be maintained in order to suck up into the blade guard that dust which is generated in the kerf and which is not thrown backwards-upwards by the tool. At the same time, dust must not be scattered to the environment from the kerf and/or due to leakage between the blade guard and the top surface of the work piece. In connection with devices which are based on this principle, however, some fundamental problems are encountered. The first problem is that the volume in the suction box, i.e. the interior volume of the hood-shaped blade guard, is comparatively large, which is a drawback because it makes it more difficult to maintain a necessary under pressure in the suction box, which in turn jeopardises its suction capacity.
U.S. Pat. No. 5,774,992 discloses a dust collecting shroud for removably attaching to a circular saw. The shroud is attached in a fixed location and will therefore pick up very little dust at the early stages of the cut before the saw reaches the set saw depth. Further the shroud arranged to suck sideways from the saw blade. Therefore the natural peripheral throw of the saw blade is not at all used. This also results in a very wide and bulky total assembly.
US 2008/0163492 shows a very different cutting and dust collecting assembly and is hereby incooperated by reference in its entirety. It has an elongated cover device of approximately the same width as its blade guard. The cover device is joined to the blade guard with a hinge, so the cover device is intended to be in contact with the structure all the time from the start of the cut until full depth of the cut. So this active hinge is a clear improvement. However inside the cover device there is a sealing that does not only decrease air leakage around the saw blade, but does also block air flow rearwards inside the cover device towards a vacuum source arranged in the rear. Instead the complete flow must follow the kerf under the block in the cover device and up into the vacuum source. This reduces the dust removal capacity considerably during all early stages of the cut before a deep kerf is established. Further such a sealing wears considerably and would need to be changed frequently. The cover device is spring loaded to swing down with its forward end. This end will therefore protrude and be a bother during transport etc. But it will also hide the saw blade, so it is difficult for the operator to start the cut correctly. Further the cover device always protrudes in front of the saw blade giving a bad visibility of the cut for the operator. All this causes using and efficiency difficulties for the operator.